G1000 BUS2 burn out

The other night I was going for a night flight in a rental Cessna 172SP with a full G1000 system when I had a disturbing BUS2 failure. I had flown the same aircraft earlier in the morning with an instructor (IFR training) and had gotten a big red X on the HDG and AHRS. The instructor simply pulled the two AHRS circuits and reset them, commenting that they did that a lot recently on this plane. The rest of the morning flight was uneventful. Later that night when I was going to go for a night VFR flight I noticed a burning electric smell shortly after turning on the avionics after a normal start. There was some ramp construction going on 40ft away from me so I was not sure if the smell was from the plane or the workers. I decided to relocate to another area to do the run up and keep an eye on the smell and electrics. The smell disappeared and the run up was uneventful. I was cleared by ground to taxi to the active (long way from ramp). About halfway there the cockpit suddenly was filled with a very strong burnt electric smell. I elected to go back to the ramp to troubleshoot and abandon the night flight idea. There were no blown circuit breakers and nothing notable about the electrical display readings.  However when I went to turn off the avionics to begin shutting the plane down I found BUS2 to be fused in the on position. Plus when I touched it (still in on position) the MFD suddenly went black and the PFD began to flicker rapidly. BUS1 would toggle off but BUS2 was firmly stuck in the on position with the burnt smell still in the air, but not as strong. I promptly pulled the mixture and turned off the master. Does anyone know what would have caused that? Could the practice of the instructor of resetting the breaker to remove red X notifications have contributed? I am concerned that I had not gone back to the ramp it could have resulted in an in flight system failure, or worse an in flight electrical fire.

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